SR
`XR
`K253879273
`United States Patent’ 1151
`Griffiths
`
`3,887,273
`[111
`[451 June 3, 197 5
`
`[54] SPEEDOMETER OPTICAL PROJECTION
`SYSTEM
`
`[75] Inventor: David Griffiths, North Plain?eld,
`N'J'
`[73] Assignee: Conrad J. Friedemann, Bloom?eld
`Hills, Mich.
`'
`July 27, 1973
`[22] Filed:
`[21] Appl. No.: 383,244
`
`[52] U.S. Cl. ..................... .. 353/14; 353/98; 353/69
`[51] Int. Cl ..................... .. G03b 21/00; G03b 21/28
`[58] Field of Search ............ .. 353/ 13, 14, 69, 11, 98
`
`[56]
`
`1,753,222
`
`References Cited
`UNITED STATES PATENTS
`4/l930 Timoney ............................. .. 353/69
`
`2,568,943
`2,935,729
`3,715,721
`
`Blaisse ................................ .. 353/69
`9/1951
`5/1960 Henss .... ..
`2/1973
`Irving .................................. .. 353/13
`
`Primary Examiner-Richard E. Aegerter
`Assistant Examiner—A. J. Mirabito
`Attorney, Agent, or Firm-Harness, Dickey & Pierce
`
`ABSTRACT
`{57}
`A system for projecting a speedometer or other instru
`ment reading as a virtual image, focused at in?nity,
`into the ?eld of view of a vehicle operator includes the
`Windshield and a lens system containing a lens that
`substantially corrects aberrations caused by curvature
`Of the Windshield.
`6 Claims, 3 Drawing Figures
`
`1
`
`ZEISS 1140
`Zeiss v. Nikon
`IPR2013-00363
`
`

`

`PfiTEQ'E'é'EDJUE-Q
`
`1975
`
`3,887,273
`
`
`
`2
`
`

`

`1
`SPEEDOMETER OPTICAL PROJECTION SYSTEM
`
`' 3,887,273
`
`2
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`BACKGROUND OF THE INVENTION
`It has long been recognized that it would be desirable
`to eliminate the need for a vehicle operator to take his
`eyes off the external scene when he wants to read the
`information presented by the instruments in the driv
`er’s compartment. As a consequence, all vehicle manu
`facturers have exerted substantial effort to place the
`instrument dials in positions that involve minimum dis
`traction and offer the best viewing advantage to the op
`erator. Additionally, systems for actually projecting
`readings by means of optical systems into the opera
`tor‘s field of view have been proposed, some of these,
`at least, being described in French Pat. No. [243,086
`and U.S. Pat. Nos. 1,871,877; 2,264,044; 2,382,631;
`2,579,806; 2,64l,l6(l; 2,685,818; 2,737,845; and
`2,738,49 l.
`Most of the known optical systems include a special
`viewing screen which is located in or close to the opera
`tor’s normal ?eld’ of vision. Such a screen is itselfa dis—
`traction and reduces the driver’s concentration on what
`is happening outside the vehicle. Other systems have
`used the windshield as a part of an optical system but
`if such systems are used in modern vehicles the image
`will be distorted and unacceptable.
`
`BRIEF SUMMARY OF THE INVENTION
`The present invention involves ( l ) the discovery that
`windshield curvature is a distorting factor in optical
`projection systems for vehicle instruments and (2) a
`means for overcoming the image distortion caused by
`the windshield when it is used as a part of the projec
`tion system.
`The invention provides the operator of a vehicle the
`means for observing his speedometer reading, or other
`selected instrument readings indicating conditions of
`his vehicle, without having to remove his gaze from the
`driving scene or to refocus his visual system. The inven
`tion provides means whereby the readings are pro
`jected optically as a virtual image focused at in?nity
`and positioned ahead of the driver. The driver thus can
`easily read the instruments without refocusing or redi
`recting his vision as he concentrates on the normal
`driving scene. The instrument readings appear at the
`periphery of the driver‘s visual ?eld.
`The invention features an optical projection system
`corrected for aberrations induced by the vehicle wind
`shield. The optical system comprises a spherical projec
`tion lens. an aberration correcting cylindrical lens. and
`the vehicle windshield. The cylindrical lens can be ei
`ther of a positive or negative focal length. The lens sys
`tem is preferably positioned below the vehicle instru
`ment panel along with the reticle to be projected. The
`reticle may be a mask in the form of a dial containing
`numerals indicating speedometer readings (or other in
`strument readings as appropriate) and is rotated or
`moved in the same manner as conventional speedome
`ter arrangements. Light from a bulb illuminates the ret
`icle. the light being transmitted through the numerals
`and projected through the optical system. The light
`source is rheostatically controlled so the proper inten
`sity of the projected image can be supplied for varying
`driving environments.
`
`5
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`DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic sectional view through a por
`tion of an automobile having a speedometer optical
`projection system embodying the invention and using
`a cylindrical lens of negative focal length;
`FIG. 2 shows a distorted image of an off-axis object
`point at in?nity as formed by a concave spherical mir
`rm; and
`FIG. 3 is a schematic view showing orientation of a
`cylindrical lens of positive focal length to correct for
`the aberrations caused by windshield curvature.
`
`DESCRIPTION OF THE INVENTION
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`to C
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`The automobile 1 has a windshield 3 which in a mod
`ern vehicle is generally not planar but is formed with
`simple and often compound curvature. Despite the cur
`vature, the windsheild can be approximately described
`as being in a plane at an angle with respect to the plane
`of the crash pad cowl 5 which is associated with the en
`gine instrument panel 7 and shelf 18, these being lo
`cated forwardly of the steering wheel 9 of the driver
`compartment 11.
`The driver is positioned behind the steering wheel 9
`- and his eye 13 is usually focused through the wind
`shield at objects located near in?nity. Normally to de
`termine the vehicle speed and other conditions of the
`vehicle, the driver must look down at the instrument
`cluster 7, focus at the close distance, locate the proper
`dial, note the reading, and then redirect and focus his
`eyes to the objects before the vehicle. During the redi
`recting and refocusing operations, the driver is subject
`to inconvenience and compromising his attention on
`road conditions. It is the purpose of this invention to
`project the instrument reading as a luminous image in
`space, formed within the normal ?eld of view of the
`driver and focused at in?nity. With the use of this in
`vention, the driver can continuously perceive and read
`the condition indicators of his vehicle as his vision is di
`rected ahead and focused on the normal driving scene.
`The system 15 includes the housing 17 which is
`mounted inside the automobile beneath the windshield
`shelf 18. The housing has a section to suit the compo
`nent parts, such as rectangular or circular with an
`adapter lens mounting. The image observed by the
`driver is a virtual image projected by the optical sys
`tem. (Note: The projection of an' imaginary speedome
`ter reading of 75 miles per hour is rotated 90° in FIG.
`1 to facilitate understanding the drawing.) The optical
`system includes the lens 19 and 21 and the windshield
`3. The latter performs the function of a mirror to the
`projection system. The lens system consists of a spheri
`cal projection lens 19 and an optical element 21 to cor
`rect for aberrations in the optical system induced by
`the windshield curvature. Together with the wind
`shield, the lens system produces parallel or collimated
`light 33 to the driver’s visual system. For this reason,
`the projected image appears to focus at in?nity.
`The reticle 23 is within housing 17 and illuminated by
`an incandescent lamp 27. The lamp and thus the bright
`ness of the projected image can be adjusted by the rhe
`ostat 29 in a suitable electrical circuit 30 so the image
`is acceptable under all ambient conditions. The reticle
`consists of a dial or scale from the speedometer (or
`other instrument gauge). It is preferable for the num~
`bers and letters on the projected dial to be bright while
`the background is dark. To achieve this, the reticle
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`3,887,273
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`preferably has transparent alphanumeric information
`on an opaque background. The reticle is driven in the _.
`conventional manner aspertains to the instrument
`I being projected; e.g., a-conventional speedometer drive
`31 connected to the automobile ‘drivetrain. To obtain
`uniform illumination of the reticle. the light is dispersed
`using a diffusing screen 32 between the light source and
`the reticle. A transparent dust cover 34'is preferably
`used over the top of the housing 17.
`If the windshield is planar, the optical projection sys
`tem may consist of only a spherical projection lens,
`preferably an achromatic lens to correct for chromatic
`aberration. The lens is placed so its back focal plane
`lies in ‘the plane of the reticle. The windshield plays the _
`role of both a planar mirror to the projection system
`vand a window to the driving environment. The lens pro
`jection housing 17 may be mounted so parallel light
`rays pass through an opening in the shelf 18 and re?ect
`from the windshield 3 into the driver‘s eyes. However, .
`in practice, the windshield surface is not planar but
`contains compound curvature. The curvature of the
`windshield affects the light rays reflected from it caus
`ing a shift in the virtual image position along with aber
`rations in the image. These aberrations cause the image
`to be blurred and distorted. It is the purpose of the in
`_ vention to provide a means to correct this condition.
`Considering the windshield as possessing ‘spherical
`curvature the situation is fundamentally described in
`FIG. 2. Image aberration occurs when a spherical mir
`ror is used to image an object lying some distance from
`the mirror axis. The result is that each ‘object point is
`imaged into two mutually perpendicular line images in
`’ stead of a point. The object in FIG. 2 is a point at infin- .
`ity and the incident rays are parallel at an angle (1) with
`respect to the mirror axis. The reflected rays are con
`verging toward two lines S and T. The re?ected rays in
`the vertical or tangential plane RAS are focused at line
`T while the rays in the horizontal or sagittal plane JAK
`focus to line S. The separation between the tangential
`‘and sagittal foci is related'to the angle d) between the
`chief ray and the mirror axis. As the obliquity of the
`rays decreases and the chief ray approaches the axis,
`the separation between S and T approaches zero and
`the lines shorten in length.
`The speedometer projection system light rays are in
`cident upon the windshield in the same manner as de
`scribed in FIG. 2. The horizontal plane .IAK of the
`windshield is across the width of the vehicle. The vehi
`cle direction is approximately along the chief ray AE.
`The effect of the windshield curvature is thus related to
`the effect of off-axis use of a spherical mirror described
`in FIG. 2; i.e., the image becomes astigmatic. Also the
`curvature causes a distinct focus shift. The focus shift
`can be corrected by altering the position of the spheri
`cal projection lens 19. Since most windshield surfaces
`are concave to the interior of the vehicle, the projected
`image is moved closer than infinity by the windshield
`curvature. The proper correction for this shift is to
`move the projection lens 19 slightly toward the reticle
`(i.e., at less than the focal length of the lens) until the
`projected image moves back to in?nity.
`The windshield curvature also produces two perpen
`dicular line images (each focusing at a different plane)
`from each point on the object as described for FIG. 2.
`The resultant best focus image appears blurred to the
`driver. The proper correcting element for this image is
`a cylindrical lens. Thus, a cylindrical lens is placed in
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`the projection optical system 15. preferably between
`the light source 27 and the spherical lens 19 for conve
`nience. It shifts the focus plane of one of the line im
`ages while not affecting the‘other. The resultant image
`again appears sharply focused to the driver.
`FIG. 1 shows the use ofa negative focal length cylin
`drical lens 21 for a compensating element. The nega
`tive lens is placed with, its power (curvature) along the
`length of the vehicle. The lens shifts the tangential
`focus farther from the driver to coincide with the sagit
`tal focus.
`I
`FIG. 3 shows the use of a positive focal length cylin
`drical lens 21’ in the projection systemJThe cylindrical
`lens is placed with its power positioned across the width
`of the vehicle. The lens shifts the sagittal focus closer
`to the driver to coincide with the tangential focus. Each
`'lens 21 and 21’ ‘is actually a segment of a cylindrical
`surface as illustrated, the negative being concave and
`the positive convex with the opposite face flat.
`Although the windshield surface is not perfectly
`spherical the compensation offered by the cylindrical
`lens 21 or 21' corrects for‘ the major part ofthe image
`aberrations and the projected image is of good quality.
`As shown in FIG. 1, the luminous, vertical, projected
`image appears to hang in space and to be at infinite fo
`cus. It is always in focus to the driver’s eyes as he navi
`gates his vehicle. The projected image is preferably po
`sitioned slightly off the center of the driver’s field of
`view, either to one side or below, so it will not be dis
`tracting.
`'
`While the invention is illustrated in conjunction with
`speedometer readings, it can be used in conjunction
`with other instrument readings of concern to the vehi
`cle operator. As the driver surveys the road ahead,
`whether he concentrates on relatively near or far ob
`jects, the speed (and other conditions of his vehicle) is
`relayed to him via an illuminated display that hangs in
`space just a short distance from the center of his for
`ward vision. Since the image is projected at infinity, it
`will always be within the depth of field of the driver’s
`eyes while he gazes at objects ahead.
`I claim:
`1. In a vehicle with an instrument panel including a
`speedometer or the like having a movable scale with
`indicia providing vehicle condition information for the
`vehicle operator, a system for projecting said informa
`tion as a luminous image at infinite focus substantially
`in the operator’s forward ?eld of view comprising a
`transparent windshield concave to the interior of the
`vehicle and of substantially spherical curvature, a pro
`jection lens for projecting parallel light rayson the in
`side surface of said transparent windshield, a light
`source for illuminating said scale and located on the
`opposite side of the scale from the lens, and an optical
`correcting element in the system for sharply focusing
`said image to overcome aberration produced by the
`curvature of the windshield, said scale being positioned
`at less than the focal length of the projection lens to
`correct for focus shift produced by curvature of the
`windshield.
`2. The invention as setforth in claim 1 wherein said
`correcting element is a cylindrical lens.
`3. The invention as set forth in claim 2 wherein said
`cylindrical lens is negative and positioned so that its
`curvature is along the length of the vehicle.
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`3,887,273
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`5
`4. The invention as set forth in claim 2 wherein said
`cylindrical lens is positive and positioned so that its cur
`vature is across the width of the vehicle.
`5. In a vehicle with an instrument panel including a
`speedometer or the like having a movable scale with
`indicia providing vehicle condition information for the
`vehicle operator, a system for projecting said informa
`tion as a luminous image at in?nite focus substantially
`in the operator’s forward field of view comprising a
`transparent windshield concave to the interior of the
`vehicle and of substantially spherical curvature, a pro
`jection lens for projecting parallel light rays on the in
`side surface of said transparent windshield, a light
`source for illuminating said scale and located on the
`opposite side of the scale from the lens, and an optical
`correcting element in the system for sharply focusing
`said image to overcome aberration produced by the
`curvature of the windshield, said correcting element
`being a negative cylindrical lens positioned so that its
`
`6
`curvature is along the length of the vehicle,
`6. In a vehicle with an instrument panel including a
`speedometer or the like having a movable scale with
`indicia providing vehicle condition information for the
`vehicle operator, a system for projecting said informa
`tion as a luminous image at in?nite focus substantially
`in the operator’s forward field of view comprising a
`transparent windshield concave to the interior of the
`vehicle and of substantially spherical curvature, a pro
`jection lens for projecting parallel light rays on the in
`side surface of said transparent windshield, a light
`source for illuminating said scale and located on the
`opposite side of the scale from the lens, and an optical
`correcting element in the system for sharply focusing
`said image to overcome aberration produced by the
`curvature of the windshield, said correcting lens being
`a positive cylindrical lens positioned so that its curva
`ture is across the width of the vehicle.
`*
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